The role of intraovarian sex hormone in mediating gonadotrophic stimulation of follicular maturation, including atresia and oogenesis has been under study in this laboratory for the past five years. These studies indicate that estrogens stimulate while androgens inhibit granulosa cell proliferation and enhance atresia during preantral stages of follicular maturation. Since ovarian biosynthesis of androgen requires LH stimulation, but biosynthesis of estradiol requires FSH stimulation as well, the role of gonadotrophins in stimulating both growth and atresia is mediated by sex steroid hormone synthesis.